1. Field of the Invention
The present invention relates to frames for backpacks.
2. Description of the Prior Art
Typically external frame style load bearing pack frames are made of rigid materials such as steel or aluminum. Fabrication techniques used to manufacture these designs generally include cutting, bending, welding and riveting together the component parts. These designs and materials emphasize strength to support heavy loads and rigidity to stabilize those loads while the wearer moves about.
Another approach used more recently is to fabricate external pack frames from molded or formed thermoplastics. These offer the benefits of reduced fabrication costs, yet compromises are made in the strength and rigidity of the frames due to the physical limitations of the polymers used.
With prior approaches that rely on steel or aluminum, there is virtually no flexing of the structure to accommodate the desired range of movements of the wearer. Additionally, straining against the rigid frame creates pressure points on the wearer that will become uncomfortable under prolonged, heavily loaded use. Rigid frame structures are not capable of absorbing catastrophic impact, and can be overwhelmed when dropped or struck. Moreover, rivets will pop, welds crack, and metal breaks when, for example, loaded packs are tossed off of trucks or strike the ground during parachute deployments. Steel or aluminum frames are expensive to manufacture.
Prior approaches that rely on molded or formed thermoplastics also have limitations. For example, frame designs using polymers are not rigid enough for the wearer to stabilize heavy loads while moving about. Thermoplastic frames can flex in unwanted ways at inopportune times, compromising the balance and therefore the safety of the user. Designs that are shaped in a manner to improve rigidity tend to compromise the desired range of motion, move the load's center-of-gravity further away from the wear's own center-of-gravity, and thus negatively impact balance and carrying comfort, creating fit conflicts with items worn on the back such as body armor plates and heavy clothing.